U.S. Pat. No. 5,080,260, by the inventor hereof, the disclosure of which is hereby incorporated by reference, discloses a bottle made of thin-walled plastic produced by blow-molding process. A bottom part is preformed with an inwardly extending, in cross section essentially V-shaped folded part which defines an elongated inner bottom fold line. The inner bottom fold line merges smoothly with body fold lines extending longitudinally of the bottle. The inner bottom fold line and the longitudinal fold line are in a single plane. The cross section of the bottle may be circular, rectangular, or hexagonal and is unitary with the pouring spout which extends, preferably with a reduced diameter, from the top portion of the bottle. Upon folding the bottle along the seam lines, and expelling all air from the inside, the bottle can be compressed and, upon tightly closing the spout, reduced to small size.
Upon blow-molding such a bottle, a seam will form at the junction of two mold parts. This, unavoidably, results in some thickening of the material. To prevent congruence of the fold with the wall thickness, it has been proposed, as described in the aforementioned patent, to place the separating plane of the blow mold form halves transversely to the longitudinal plane of the bottle. This results in excellent foldability of the bottle.
It has been found that shifting the separating plane of the blow mold in bottles in which a handle is formed inherently and as part of the bottle does not make it possible to place the seam line transversely to the bottom fold, since it would no longer be possible to remove the blow-molded bottle from the blow mold form and, further, the two halves of the blow-mold form would not be mirror-symmetrical. Otherwise, expensive multiple-part special forms, with sliders and the like, would have to be used, which makes manufacture of such a bottle expensive.
If the same folding principle as that described in the earlier U.S. Pat. No. 5,080,260 is carried out in bottles in which the entire separating plane of the bottle halves or, rather, of the mold halves, are placed in a longitudinal plane of the bottle which coincides with a central plane, also including the bottom fold line, the separating thickening of the bottle becomes congruent with the bottom fold line. This is undesirable, since it interferes with folding. In the manufacture of bottles of this type, a hot extruded tube of plastic material is gripped by two form halves, and compressed in the region of the pinch edges of the mold halves. At the ends of the respective pinch seams, then, material from the plastic tube will accumulate. This material has roughly crescent-moon shape. The thickening of the material in the region of the bottom of the bottle can be a multiple, and it has been found typically up to six times the normal wall thickness. This accumulation of material, practically unavoidable in blow-molding, interferes with folding of the bottom of the bottle along its longitudinal plane; in extreme cases, and excessive accumulation of material, may make folding the bottle impossible. The accumulation of material upon blow-molding the bottle is located inwardly, at least in part, within the inverted V-shaped bottom of the bottle. Thus, the thickening of the material does not enhance the support of the bottle, for example on a support surface such as a shelf or table, and does not contribute to stabilizing the weight of the bottle.